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Unseptoctium
Unseptoctium, Uso, is the temporary name for element 178. NUCLEAR What follows is based on a first-order, liquid-drop assessment of where the outer boundary of the nuclear world is. Assume cautious values for how many neutrons a nucleus with 178 protons can bind (high neutron dripline) and how few it can have before it fissions immediately regardless of how much the structure it can develop stabilizes it (low must-fission curve). Assume, too, that anything that lasts long enough so that protons and neutrons can be treated as particles rather than collections of quarks (is causal) might be a nucleus. Under these conditions, Uso isotopes are theoretically possible between Uso 428 and Uso 775 (see "The Final Element", this wiki). Uso 428 through Uso 622 are expected to decay by beta emission if they don’t fission quickly. Above that value of A, the confident neutron dripline, drops may decay by neutron emission before they can fission. (Structural correction does not affect neutron emission.) Uso 622 itself requires 1.5 MeV of structural correction energy to survive for the 10^-14 sec needed to bind an electron and so qualify as a nucleus. Uso 693 and heavier don’t require any correction. Isotopes lighter than Uso 452 need more than twice the correction energy needed to prevent fission in worst-case nuclei in the A = 480 region(1). In between, it is not usually possible to determine whether structural corrections will stabilize nuclear drops against fission. Neutron shell closures have been predicted at N = 406(2),(3),(4), 370(4), 318(5), and 308(1). The isotope Uso 584 requires 1.5 MeV of structural correction, which means all isotopes in the Uso 574 to Uso 589 band are likely. Uso 548 requires 3 MeV of structural correction, which means all isotopes in the band Uso 538 to Uso 553 are also likely. Long beta-decay half-lives are possible for Uso 538 and Uso 539, so decay by alpha emission is possible in that portion of the band, with beta decay expected in the remainder. Uso 496 requires 10.5 MeV of correction energy, and Uso 486 requires 13.5 MeV, which implies that some nuclides in the band Uso 476 to Uso 501 are possible if correction is strong. Alpha decay is to be expected in this band. Between Uso 452 and Uso 647 some drops may be nuclei. Outside this band, isotopes of Uso are nearly impossible. ATOMIC Electron structure of Uso has not been studied closely, but it is likely to differ significantly from the conventional orbitals found in lower-Z nuclei. While only the innermost electrons would be qualitatively different, other electrons are likely to be quantitatively different from those in lower-Z atoms. Uso is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Uso to have different electronic structures. (That means it is no longer an element in the chemical sense.) Predictions of atomic or chemical properties of Uso are risky. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. It is probably impossible for lighter isotopes to form in this way. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Uso 574 to Uso 577 to form. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uso 574 to Uso 589, Uso 538 to Uso 553, and Uso 476 to Uso 501 bands. Quantities produced by this method are very small. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 3. “Search for Superheavy Elements Among Fossil Fission Tracks in Zircon”; J. Maly & D.R. Walz; Stanford Linear Accelerator Center publication SLAC-PUB-2554; July 1980. 4. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 5. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-08-19)